Composition for energy storage device, slurry for energy storage device electrode, energy storage device electrode, and energy storage device

Abstract

To provide a composition for a power storage device, which suppresses occurrence of electrode corrosion and decomposition of thickeners by preventing temporal pH increase in slurry for a power storage device electrode, and can improve adhesion and charge / discharge endurance characteristics of a power storage device electrode.SOLUTION: A composition for a power storage device according to the present invention contains a polymer particle (A) and a liquid medium (B). When the total of repeating units that are included in the polymer particle (A) is 100 mass%, the polymer particle (A) contains 5-50 mass% of repeating units (a1) derived from an unsaturated carboxylic acid ester with a hydroxyl group, and 50-90 mass% of repeating units (a2) derived from an unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester with a hydroxyl group). At least a part of a hydroxyl group contained in the unsaturated carboxylic acid ester with a hydroxyl group is protected with a protecting group.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a composition for a power storage device, a slurry for a power storage device electrode, a power storage device electrode, and a power storage device.

Background Art

[0002] In recent years, as a power source for driving electronic devices, a power storage device having a high voltage and a high energy density has been demanded. As such a power storage device, a lithium ion battery, a lithium ion capacitor, etc. are expected.

[0003] An electrode used in such a power storage device is manufactured by applying and drying a composition (slurry for a power storage device electrode) containing an active material and a polymer functioning as a binder on the surface of a current collector. The characteristics required for the polymer used as the binder include the binding ability between the active materials, the adhesion ability between the active material and the current collector, the abrasion resistance in the process of winding the electrode, and the powder dropout resistance that prevents fine powder of the active material from dropping off from the applied and dried composition coating film (hereinafter also referred to as the "active material layer") even by subsequent cutting, etc. By such a binder material exhibiting good adhesion and reducing the internal resistance of the battery caused by the binder material, good charge and discharge characteristics can be imparted to the power storage device.

[0004] Note that, regarding the above-mentioned binding ability between the active materials, the adhesion ability between the active material and the current collector, and the powder dropout resistance, it has been empirically clarified that the quality of the performance is almost in a proportional relationship. Therefore, in this specification, these may be collectively referred to as "adhesion" using the term hereinafter.

[0005] Recently, in order to fabricate an electrochemical device having excellent capacity and charge-discharge cycle characteristics, research has been conducted on using an active material having high reactivity with water. And when manufacturing a slurry for a power storage device electrode containing an active material and a binder, the use of an aqueous binder has been studied for the purpose of cost reduction, safety improvement, and environmental load reduction.

[0006] Under such circumstances, various binder materials have been proposed to solve the problems of slurries for electrodes of energy storage devices (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, when using slurries for electrodes of energy storage devices containing the binder materials disclosed in Patent Documents 1 and 2 above, there were several problems. For example, water in the slurry reacts with the active material to generate hydroxide ions (OH - ), which can cause corrosion of the electrode and decomposition of the thickener. In addition, the electrodes of energy storage devices produced using such slurries for electrodes of energy storage devices were not sufficient in terms of properties such as adhesion and charge-discharge durability characteristics, and further improvement was required.

[0009] Some aspects of the present invention provide a composition for a power storage device that can prevent an increase in pH over time of a slurry for a power storage device electrode, suppress the occurrence of corrosion of the electrode or the decomposition of a thickener, and improve the adhesion and charge / discharge durability characteristics of the power storage device electrode. Further, some aspects of the present invention provide a slurry for a power storage device electrode that can prevent a change in pH over time, suppress the occurrence of corrosion of the electrode or the decomposition of a thickener, and improve the adhesion and charge / discharge durability characteristics of the power storage device electrode. Additionally, some aspects of the present invention provide a power storage device electrode in which corrosion is suppressed and the adhesion and charge / discharge durability characteristics can be improved. Furthermore, some aspects of the present invention provide a power storage device having excellent charge / discharge durability characteristics.

Means for Solving the Problems

[0010] The present invention has been made to solve at least a part of the above-described problems and can be realized as any of the following aspects.

[0011] One aspect of the composition for a power storage device according to the present invention is containing polymer particles (A) and a liquid medium (B), when the total of the repeating units contained in the polymer particles (A) is 100% by mass, the polymer particles (A) are containing 5 to 50% by mass of a repeating unit (a1) derived from an unsaturated carboxylic acid ester having a hydroxyl group, and 50 to 90% by mass of a repeating unit (a2) derived from an unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester having a hydroxyl group), and at least a part of the hydroxyl groups contained in the unsaturated carboxylic acid ester having a hydroxyl group is protected by a protecting group.

[0012] In one aspect of the composition for a power storage device, the number average particle diameter of the polymer particles (A) may be 50 nm or more and 1000 nm or less.

[0013] In any aspect of the composition for the power storage device, The protecting group may be deprotected by the action of a base.

[0014] In any aspect of the composition for the power storage device, The protecting group may be an acyl group.

[0015] In any aspect of the composition for the power storage device, The polymer particles (A) may further contain 1 to 20% by mass of a repeating unit (a3) derived from an unsaturated carboxylic acid.

[0016] In any aspect of the composition for the power storage device, The polymer particles (A) may further contain 1 to 30% by mass of a repeating unit (a4) derived from an aromatic vinyl compound.

[0017] In any aspect of the composition for the power storage device, The surface acid amount of the polymer particles (A) may be 0.05 mmol / g or more and 6 mmol / g or less.

[0018] In any aspect of the composition for the power storage device, When the polymer particles (A) are immersed in a solvent composed of propylene carbonate and diethyl carbonate at a volume fraction of 1:1 under the conditions of 70°C for 24 hours, The swelling ratio may be 130% by mass or more and 350% by mass or less.

[0019] In any aspect of the composition for the power storage device, The liquid medium (B) may be water.

[0020] One aspect of the slurry for the power storage device electrode according to the present invention is It contains the composition for the power storage device in any of the above aspects and an active material.

[0021] In one embodiment of the slurry for the power storage device electrode, it may further contain a thickener.

[0022] In any embodiment of the slurry for the power storage device electrode, as the active material, it may contain at least one selected from the group consisting of an olivine-type lithium-containing phosphate compound, lithium cobaltate, lithium nickelate, lithium manganate, and lithium nickel cobalt manganate.

[0023] In any embodiment of the slurry for the power storage device electrode, as the active material, it may contain a lithium compound and a silicon compound having oxygen.

[0024] One embodiment of the power storage device electrode according to the present invention is comprising a current collector and an active material layer formed by applying and drying the slurry for the power storage device electrode in any of the above embodiments on the surface of the current collector.

[0025] One embodiment of the power storage device according to the present invention is comprising the power storage device electrode in the above embodiment.

Advantages of the Invention

[0026] According to the composition for a power storage device of the present invention, by preventing the pH of the slurry for the power storage device electrode from rising over time, the occurrence of corrosion of the electrode or the decomposition of the thickener is suppressed, and a power storage device electrode excellent in adhesion and charge-discharge durability characteristics can be manufactured.

Embodiments for Carrying Out the Invention

[0027] Hereinafter, preferred embodiments according to the present invention will be described in detail. It should be understood that the present invention is not limited only to the embodiments described below, but also includes various modifications implemented within the scope without changing the gist of the present invention.

[0028] As used herein, “(meth)acrylic acid~” is a concept that encompasses both “acrylic acid~” and “methacrylic acid~”. Further, “~(meth)acrylate” is a concept that encompasses both “~acrylate” and “~methacrylate”.

[0029] 1. Composition for a power storage device The composition for a power storage device according to one embodiment of the present invention contains polymer particles (A) and a liquid medium (B). When the total of the repeating units contained in the polymer particles (A) is 100% by mass, the polymer particles (A) contain 5 to 50% by mass of a repeating unit (a1) derived from an unsaturated carboxylic acid ester having a hydroxyl group, and 50 to 90% by mass of a repeating unit (a2) derived from an unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester having a hydroxyl group). At least a part of the hydroxyl groups contained in the unsaturated carboxylic acid ester having a hydroxyl group is protected by a protecting group. Hereinafter, each component contained in the composition for a power storage device according to the present embodiment will be described in detail.

[0030] 1.1. Polymer particles (A) The composition for a power storage device according to the present embodiment contains polymer particles (A). When the total of the repeating units contained in the polymer particles (A) is 100% by mass, the polymer particles (A) contain 5 to 50% by mass of a repeating unit (a1) (hereinafter, also simply referred to as “repeating unit (a1)”) derived from an unsaturated carboxylic acid ester having a hydroxyl group, and 50 to 90% by mass of a repeating unit (a2) (hereinafter, also simply referred to as “repeating unit (a2)”) derived from an unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester having a hydroxyl group). Further, in addition to the repeating units (a1) and (a2), the polymer particles (A) may contain repeating units derived from other monomers copolymerizable therewith.

[0031] The polymer particles (A) contained in the composition for a power storage device according to this embodiment exist in a latex state dispersed in a liquid medium (B). When the polymer particles (A) are in a latex state dispersed in the liquid medium (B), the stability of the slurry for a power storage device electrode (hereinafter also simply referred to as "slurry") produced by mixing with an active material is good, and the coatability of the slurry on a current collector is good, which is preferable.

[0032] Hereinafter, the repeating unit constituting the polymer particles (A), the physical properties of the polymer particles (A), and the production method will be described in this order.

[0033] 1.1.1. Repeating unit constituting polymer particles (A) 1.1.1.1. Repeating unit (a1) derived from an unsaturated carboxylic acid ester having a hydroxyl group The polymer particles (A) contain a repeating unit (a1) derived from an unsaturated carboxylic acid ester having a hydroxyl group. The content ratio of the repeating unit (a1) derived from an unsaturated carboxylic acid ester having a hydroxyl group is 5 to 50% by mass when the total of the repeating units contained in the polymer particles (A) is 100% by mass. The lower limit of the content ratio of the repeating unit (a1) is preferably 7% by mass, more preferably 10% by mass. The upper limit of the content ratio of the repeating unit (a1) is preferably 49% by mass, more preferably 48% by mass. When the polymer particles (A) contain the repeating unit (a1) within the above range, the dispersibility of the active material becomes good, and it becomes possible to produce a uniform active material layer. As a result, the structural defects of the electrode plate disappear, and good charge-discharge characteristics are exhibited.

[0034] Among the unsaturated carboxylic acid esters having a hydroxyl group, (meth)acrylic acid esters having a hydroxyl group can be preferably used. Specific examples of the (meth)acrylic acid esters having a hydroxyl group include, for example, hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, glycerin mono(meth)acrylate, glycerin di(meth)acrylate, etc. One or more selected from these can be used. Among these, it is preferably one or more selected from 2-hydroxyethyl (meth)acrylate, glycerin mono(meth)acrylate, and glycerin di(meth)acrylate, and particularly preferably 2-hydroxyethyl (meth)acrylate.

[0035] At least a part of the hydroxyl groups possessed by the repeating unit (a1) is protected by a protecting group. When a liquid medium mainly composed of water is used to prepare a slurry, water reacts with the active material to generate hydroxide ions, and the pH shifts to the basic side, resulting in problems such as electrode corrosion and inhibition of the function of the thickener. The composition for an electricity storage device according to the present embodiment contains polymer particles (A) having a repeating unit (a1). By capturing and deprotecting the hydroxide ions, where the protecting group in the repeating unit (a1) is a base, the hydroxide ions in the system are consumed, and the pH increase of the slurry over time can be prevented. Thereby, the occurrence of electrode corrosion and the reduction of the function of the thickener can be effectively suppressed.

[0036] The protecting group is not particularly limited as long as it can be used as a protecting group for a hydroxyl group, but it is preferably one that is hydrolyzed by the action of a base to undergo deprotection. Examples of such protecting groups include trihydrocarbylsilyl groups such as trimethylsilyl group and tert-butyldimethylsilyl group; acyl groups such as acetyl group, benzoyl group, and pival group. Among these, an acyl group is preferred in order to facilitate the introduction into the repeating unit (a1).

[0037] Examples of the acyl group include aliphatic acyl groups and aromatic acyl groups. The aliphatic acyl group may be linear or branched, and a linear one is preferred in order to improve both solubility in an organic solvent and water solubility. Also, the aliphatic acyl group may be saturated or unsaturated, and a saturated one is preferred in order to improve oxidation resistance. The number of carbon atoms of the aliphatic acyl group is preferably 2 to 20, more preferably 2 to 15, and still more preferably 2 to 10 in order to improve both solubility in an organic solvent and water solubility. The aliphatic hydrocarbon group in the aliphatic acyl group may have a heteroatom such as oxygen, nitrogen, sulfur, fluorine, chlorine, bromine, or silicon. Specific examples of the aliphatic acyl group include acyl groups derived from fatty acids such as acetic acid, propionic acid, and pivalic acid. Also, the aromatic acyl group is not particularly limited as long as it is an acyl group derived from an aromatic carboxylic acid. The number of carbon atoms of the aromatic acyl group is preferably 6 to 20, more preferably 6 to 15, and still more preferably 6 to 10 in order to improve both solubility in an organic solvent and water solubility. The aromatic hydrocarbon group in the aromatic acyl group may have a heteroatom such as oxygen, nitrogen, sulfur, fluorine, chlorine, bromine, or silicon. Specific examples of the aromatic acyl group include acyl groups derived from aromatic carboxylic acids such as benzoic acid, 4-methoxybenzoic acid, naphthalene-1-carboxylic acid, and naphthalene-2-carboxylic acid.

[0038] These protecting groups may be used alone or in any combination of two or more.

[0039] The substitution rate of the hydroxyl group in the repeating unit (a1) by a protecting group (hereinafter also referred to as "substitution rate of the hydroxyl group") is preferably 30 mol% or more, more preferably 45 mol% or more, and particularly preferably 65 mol% or more in order to suppress the increase in the slurry pH. And in order to simplify the synthesis, it is preferably 99 mol% or less, more preferably 98 mol% or less, and particularly preferably 97 mol% or less. The substitution rate of the hydroxyl group can be calculated using the solid content concentration, gas chromatography or 1 1H-NMR, and specifically can be calculated by the method described in the examples. By setting the substitution rate of the hydroxyl group within the above range, the increase in the pH of the slurry over time can be prevented, and as a result, the occurrence of electrode corrosion and the deterioration of the function of the thickener can be effectively suppressed.

[0040] As a method for substituting the hydroxyl group in the repeating unit (a1) with a protecting group, there is a method of reacting the repeating unit (a1) with a compound for introducing a protecting group. Examples of the compound for introducing an acyl group include, for example, R 1 -(C=O)-X (R 1 represents a linear or branched alkyl group or alkenyl group, or an aryl group, and X represents a halogen atom) or R 1 -(C=O)-O-(C=O)-R 1 (R 1 is the same as above, and a plurality of R 1 may be the same or different).

[0041] The timing of substituting the hydroxyl group in the repeating unit (a2) with a protecting group may be simultaneous with the production of the polymer particles (A) or after the production of the polymer particles (A). As an example of being simultaneous with the production of the polymer particles (A), in the method for producing the polymer particles (A) described later A method of reacting a monomer mixture, a suitable emulsifier, a chain transfer agent, and a compound for introducing the protecting group together with a polymerization initiator; a method of reacting a compound for introducing the protecting group after completion of the emulsion polymerization and before adding a neutralizing agent; and a method of reacting a compound for introducing the protecting group after adding a neutralizing agent can be mentioned. When reacting a compound for introducing the protecting group after completion of the emulsion polymerization, an organic solvent in which the compound for introducing the protecting group is dissolved may be present. Examples of such organic solvents include aliphatic hydrocarbon solvents such as pentane, hexane, and octane; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; halogen solvents such as dichloromethane and 1,2-dichloroethane; amide solvents such as N,N-dimethylformamide and N,N-dimethylacetamide; ether solvents such as tetrahydrofuran, diethyl ether, 1,2-dimethoxyethane, diglyme, and triglyme; ketone solvents such as acetone, dibutyl ketone, and methyl isobutyl ketone; nitrile solvents such as acetonitrile, propanenitrile, and benzonitrile, etc. However, there is no particular limitation as long as it is a solvent in which the compound for introducing the protecting group is dissolved. These organic solvents may be used alone or in a mixture of two or more.

[0042] On the other hand, as an example where the timing of substituting the hydroxyl group of the repeating unit (a1) with a protecting group is after the production of the polymer particles (A), a method of adding a compound for introducing the protecting group dissolved in a suitable organic solvent to the polymerization mixture can be mentioned. Such an organic solvent can be appropriately selected from among organic solvents in which the compound for introducing the protecting group is dissolved. However, since the polymer particles (A) dissolve and the reaction efficiency can be improved, tetrahydrofuran, acetone, and acetonitrile are preferable.

[0043] At this time, if necessary, nitrogen-containing compounds having no N-H bond such as tertiary amines, amidine compounds, diazabicyclo[2,2,2]octane, pyridine, and 4-dimethylaminopyridine; metal hydroxides such as sodium hydroxide and potassium hydroxide may be added.

[0044] Further, the polymer particles (A) can also be obtained by polymerizing an unsaturated carboxylic acid ester in which at least a part of the hydroxyl group is protected by a protecting group (hereinafter also referred to as "unsaturated carboxylic acid ester containing a protecting group and a hydroxyl group").

[0045] Examples of the unsaturated carboxylic acid ester containing a protecting group and a hydroxyl group include compounds in which at least a part of the hydroxyl group of the unsaturated carboxylic acid ester containing a hydroxyl group described in the repeating unit (a1) is protected by the above-described protecting group.

[0046] 1.1.1.2. Repeating unit (a2) derived from an unsaturated carboxylic acid ester The polymer particles (A) contain a repeating unit (a2) derived from an unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester having the hydroxyl group). When the total of the repeating units contained in the polymer particles (A) is 100% by mass, the content ratio of the repeating unit (a2) is 50 to 90% by mass. The lower limit of the content ratio of the repeating unit (a2) is preferably 52% by mass, more preferably 53% by mass. The upper limit of the content ratio of the repeating unit (a2) is preferably 89% by mass, particularly preferably 88% by mass. When the polymer particles (A) contain the repeating unit (a2) within the above range, the affinity between the polymer particles (A) and the electrolytic solution becomes better, and an increase in the internal resistance due to the polymer particles (A) becoming an electric resistance component in the power storage device can be suppressed. Further, a decrease in the binding property between the active material layer and the current collector due to the polymer particles (A) excessively absorbing the electrolytic solution can be more effectively suppressed.

[0047] Among the unsaturated carboxylic acid esters, (meth)acrylic acid esters can be preferably used. Examples of the (meth)acrylic acid ester include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, (meth)acrylic acid Isopropyl, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, etc. may be mentioned, and one or more selected from these can be used. Among these, one or more selected from methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate and ethylene glycol di(meth)acrylate are preferable, and 2-ethylhexyl (meth)acrylate and cyclohexyl (meth)acrylate are particularly preferable.

[0048] 1.1.1.3. Other repeating units In addition to the repeating units (a1) and (a2), the polymer particles (A) may contain repeating units derived from other monomers copolymerizable therewith. Examples of such repeating units include repeating units (a3) derived from unsaturated carboxylic acids (hereinafter also simply referred to as "repeating units (a3)"), repeating units (a4) derived from aromatic vinyl compounds (hereinafter also simply referred to as "repeating units (a4)"), repeating units (a5) derived from (meth)acrylamide (hereinafter also simply referred to as "repeating units (a5)"), repeating units (a6) derived from α,β-unsaturated nitrile compounds (hereinafter also simply referred to as "repeating units (a6)"), repeating units (a7) derived from compounds having a sulfonic acid group (hereinafter also simply referred to as "repeating units (a7)"), repeating units derived from cationic monomers, and the like.

[0049] <Repeating unit (a3) derived from unsaturated carboxylic acid> The polymer particles (A) may contain a repeating unit (a3) derived from an unsaturated carboxylic acid. The content ratio of the repeating unit (a3) derived from an unsaturated carboxylic acid is preferably 1 to 20% by mass when the total of the repeating units contained in the polymer particles (A) is 100% by mass. The lower limit of the content ratio of the repeating unit (a3) is more preferably 3% by mass, and particularly preferably 5% by mass. The upper limit of the content ratio of the repeating unit (a3) is more preferably 19% by mass, and particularly preferably 18% by mass. When the polymer particles (A) contain the repeating unit (a3) within the above range, the stability of the polymer particles (A) is excellent during the preparation of the slurry for the electrode of the power storage device, so that aggregates are less likely to occur. In addition, the increase in the slurry viscosity over time can also be suppressed. Further, the dispersibility of the active material becomes good, and a uniform active material layer can be formed, so that structural defects of the electrode plate disappear and good charge-discharge characteristics are exhibited. Furthermore, when an active material containing a silicon material is used, the binding ability between the active materials can be enhanced, so that an active material layer excellent in flexibility and adhesion to the current collector can be obtained.

[0050] The unsaturated carboxylic acid is not particularly limited, and examples thereof include monocarboxylic acids and dicarboxylic acids (including anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, and one or more selected from these can be used. As the unsaturated carboxylic acid, it is preferable to use one or more selected from acrylic acid, methacrylic acid, and itaconic acid.

[0051] <Repeating unit (a4) derived from an aromatic vinyl compound> The polymer particles (A) may contain a repeating unit (a4) derived from an aromatic vinyl compound. The content ratio of the repeating unit (a4) derived from an aromatic vinyl compound is the polymer particles When the total of the repeating units contained in (A) is 100% by mass, it is preferably 1 to 30% by mass. The lower limit of the content ratio of the repeating unit (a4) is more preferably 2% by mass, and particularly preferably 5% by mass. The upper limit of the content ratio of the repeating unit (a4) is more preferably 27% by mass, and particularly preferably 25% by mass. When the polymer particles (A) contain the repeating unit (a4) within the above range, they can exhibit good adhesion to active materials and the like, and a storage device electrode excellent in flexibility and adhesion may be obtained.

[0052] The aromatic vinyl compound is not particularly limited, and examples thereof include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene, etc., and one or more selected from these can be used.

[0053] When the polymer particles (A) contain both the repeating unit (a3) and the repeating unit (a4), when the total of the repeating units contained in the polymer particles (A) is 100% by mass, the total amount of the repeating unit (a3) and the repeating unit (a4) is preferably 45% by mass or less, more preferably 40% by mass or less, and particularly preferably 37% by mass or less. When the total amount of the repeating unit (a3) and the repeating unit (a4) is within the above range, the dispersibility of the active material becomes good, and the flexibility and adhesion are improved, so that good charge-discharge cycle characteristics and charge-discharge durability characteristics are exhibited.

[0054] <Repeating unit (a5) derived from (meth)acrylamide> The polymer particles (A) may contain a repeating unit (a5) derived from (meth)acrylamide. When the total of the repeating units contained in the polymer particles (A) is 100% by mass, the content ratio of the repeating unit (a5) is preferably 0 to 10% by mass. The lower limit of the content ratio of the repeating unit (a5) is more preferably 1% by mass, and particularly preferably 2% by mass. The upper limit of the content ratio of the repeating unit (a5) is more preferably 8% by mass, and particularly preferably 5% by mass. When the polymer particles (A) contain the repeating unit (a5) within the above range, the dispersibility of the active material and the filler in the slurry may be improved. In addition, the flexibility of the obtained active material layer may become appropriate, and the adhesion between the current collector and the active material layer may be improved. Furthermore, since the binding ability between the active materials containing a silicon material can be enhanced, an active material layer having better flexibility and adhesion to the current collector may be obtained.

[0055] (Meth)acrylamide is not particularly limited, and examples thereof include acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide, N,N-dimethylaminopropylacrylamide, N,N-dimethylaminopropylmethacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, diacetoneacrylamide, maleic amide, acrylamide tert-butylsulfonic acid, etc. One or more selected from these can be used.

[0056] <Repeating unit (a6) derived from an α,β-unsaturated nitrile compound> The polymer particles (A) may contain a repeating unit (a6) derived from an α,β-unsaturated nitrile compound. The content ratio of the repeating unit (a6) is preferably 0 to 60% by mass when the total of the repeating units contained in the polymer particles (A) is 100% by mass. The lower limit of the content ratio of the repeating unit (a6) is more preferably 0.5% by mass, and particularly preferably 1% by mass. The upper limit of the content ratio of the repeating unit (a6) is more preferably 55% by mass, and particularly preferably 50% by mass. By containing the repeating unit (a6) in the above range in the polymer particles (A), the dissolution of the polymer particles (A) in the electrolytic solution can be reduced. This makes it possible to improve the affinity between the polymer particles (A) and the electrolytic solution, facilitate the insertion and extraction of Li ions, and may exhibit good charge-discharge characteristics.

[0057] The α,β-unsaturated nitrile compound is not particularly limited, and examples thereof include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide, etc., and one or more selected from these can be used. Among these, one or more selected from the group consisting of acrylonitrile and methacrylonitrile are preferable, and acrylonitrile is particularly preferable.

[0058] <Repeating unit (a7) derived from a compound having a sulfonic acid group> The polymer particles (A) may contain a repeating unit (a7) derived from a compound having a sulfonic acid group. The content ratio of the repeating unit (a7) is preferably 0 to 10% by mass when the total of the repeating units contained in the polymer particles (A) is 100% by mass. The lower limit of the content ratio of the repeating unit (a7) is more preferably 0.5% by mass, and particularly preferably 1% by mass. The upper limit of the content ratio of the repeating unit (a7) is more preferably 8% by mass, and particularly preferably 5% by mass. By containing the repeating unit (a7) in the above range in the polymer particles (A), the dispersibility of the active material becomes good, and a uniform active material layer can be formed, so that the structural defects of the electrode plate are eliminated, and good charge-discharge characteristics may be exhibited.

[0059] Examples of the compound having a sulfonic acid group include, but are not particularly limited to, compounds such as vinylsulfonic acid, styrenesulfonic acid, allylsulfonic acid, sulfoethyl (meth)acrylate, sulfopropyl (meth)acrylate, sulfobutyl (meth)acrylate, 2-acrylamido-2-methylpropanesulfonic acid, 2-hydroxy-3-acrylamidopropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and alkali salts thereof. One or more of these can be used.

[0060] <Repeating unit derived from a cationic monomer> The polymer particles (A) may contain repeating units derived from a cationic monomer. The cationic monomer is not particularly limited, but is preferably at least one monomer selected from the group consisting of secondary amine (salt), tertiary amine (salt), and quaternary ammonium salt. Specific examples of these cationic monomers are not particularly limited, but include 2-(dimethylamino)ethyl (meth)acrylate, methyl 4-quaternary salt of dimethylaminoethyl (meth)acrylate chloride, 2-(diethylamino)ethyl (meth)acrylate, 3-(dimethylamino)propyl (meth)acrylate, 3-(diethylamino)propyl (meth)acrylate, 4-(dimethylamino)phenyl (meth)acrylate, 2-[(3,5-dimethylpyrazolyl)carbonylamino]ethyl (meth)acrylate, 2-(0-[1'-methylpropylideneamino]carboxamido)ethyl (meth)acrylate, 2-(1-aziridinyl)ethyl (meth)acrylate, methacryloylcholine chloride, tris(2-acryloyloxyethyl) isocyanurate, 2-vinylpyridine, quinacridine red, 1,2-di(2-pyridyl)ethylene, 4'-hydrazino-2-stilbazoles dihydrochloride hydrate, 4-(4-dimethylaminostyryl)quinoline, 1-vinylimidazole, diallylamine, diallylamine hydrochloride, triallylamine, diallyldimethylammonium chloride, dichloramide, N-allylbenzylamine, N-allylaniline, 2,4-diamino-6-diallylamino-1,3,5-triazine, N-trans-cinnamyl-N-methyl-(1-naphthylmethyl)amine hydrochloride, trans-N-(6,6-dimethyl-2-hepten-4-ynyl)-N-methyl-1-naphthylmethylamine hydrochloride, etc. One or more selected from these can be used.

[0061] 1.1.2. Physical properties of the polymer particles (A) 1.1.2.1. Number average particle diameter The number average particle diameter of the polymer particles (A) is preferably 50 nm or more and 1000 nm or less. The lower limit of the number average particle diameter is more preferably 60 nm, and particularly preferably 70 nm. The upper limit of the number average particle diameter is more preferably 950 nm, and particularly preferably 900 nm. When the number average particle diameter of the polymer particles (A) is within the above range, the polymer particles (A) are likely to adsorb on the surface of the active material, so that the polymer particles (A) can also move following the movement of the active material. As a result, migration can be suppressed, and thus deterioration of electrical characteristics may be reduced. The number average particle diameter of the polymer particles (A) can be measured by the method described in the examples below.

[0062] 1.1.2.2. Surface acid amount The surface acid amount of the polymer particles (A) is preferably 0.05 mmol / g or more and 6 mmol / g or less. The lower limit of the surface acid amount is more preferably 0.06 mmol / g, and particularly preferably 0.07 mmol / g. The upper limit of the surface acid amount is more preferably 5.8 mmol / g, and particularly preferably 5.5 mmol / g. When the surface acid amount of the polymer particles (A) is within the above range, a stable and homogeneous slurry can be prepared. When an active material layer is prepared using such a homogeneous slurry, an active material layer with small thickness variation in which the active material and the polymer particles (A) are uniformly dispersed can be obtained. As a result, variations in charge-discharge characteristics within the electrode can be suppressed, and thus a power storage device exhibiting good charge-discharge characteristics can be obtained.

[0063] 1.1.2.3. Swelling ratio When the polymer particles (A) are immersed in a solvent composed of propylene carbonate and diethyl carbonate at a volume ratio of 1:1 under the conditions of 70 °C for 24 hours, the swelling ratio is preferably 130% by mass or more and 350% by mass or less. The lower limit of the swelling ratio is more preferably 135% by mass, and particularly preferably 140% by mass. The upper limit of the swelling ratio is more preferably 345% by mass, and particularly preferably 340% by mass. When the swelling ratio is within the above range, the polymer particles (A) can swell moderately with respect to the electrolyte solution. As a result, the solvated lithium ions can easily reach the active material, reducing the internal resistance of the electrode and realizing better charge-discharge cycle characteristics. Also, if the swelling ratio is within the above range, no large volume change occurs, so the adhesion is also excellent. The swelling ratio of the polymer particles (A) can be measured by the method described in the examples below.

[0064] 1.1.3. Method for producing polymer particles (A) The method for producing the polymer particles (A) is not particularly limited, but for example, it can be carried out by an emulsion polymerization method in the presence of a known emulsifier (surfactant), chain transfer agent, polymerization initiator, etc. As the emulsifier (surfactant), chain transfer agent, and polymerization initiator, the compounds described in Japanese Patent No. 5999399 and the like can be used.

[0065] The emulsion polymerization method for synthesizing the polymer particles (A) may be carried out by one-stage polymerization or by multi-stage polymerization of two or more stages.

[0066] When the synthesis of the polymer particles (A) is carried out by one-stage polymerization, the above monomer mixture can be subjected to emulsion polymerization in the presence of a suitable emulsifier, chain transfer agent, polymerization initiator, etc., preferably at 40 to 80 °C, and preferably for 4 to 36 hours.

[0067] When the synthesis of the polymer particles (A) is carried out by two-stage polymerization, the polymerization in each stage is preferably set as follows.

[0068] The usage ratio of the monomer used in the first-stage polymerization is 20 to 100 mass %, preferably in the range of 25 to 100 mass %, more preferably in the range of 25 to 100 mass %. By performing the first-stage polymerization at such a usage ratio of the monomer, polymer particles (A) with excellent dispersion stability and hardly generating aggregates can be obtained, and the increase in viscosity of the composition for the power storage device over time can also be suppressed, which is preferable.

[0069] The type and usage ratio of the monomer used in the second-stage polymerization may be the same as or different from the type and usage ratio of the monomer used in the first-stage polymerization.

[0070] The polymerization conditions at each stage are preferably as follows in order to improve the dispersibility of the resulting polymer particles (A). · First-stage polymerization: preferably at a temperature of 40 to 80 °C; preferably a polymerization time of 2 to 36 hours; preferably a polymerization conversion rate of 50 mass % or more, more preferably 60 mass % or more. · Second-stage polymerization: preferably at a temperature of 40 to 80 °C; preferably a polymerization time of 2 to 18 hours.

[0071] By setting the total solid content concentration in the emulsion polymerization to 50 mass % or less, the polymerization reaction can proceed with good dispersion stability of the resulting polymer particles (A). This total solid content concentration is preferably 48 mass % or less, more preferably 45 mass % or less.

[0072] Even when the synthesis of the polymer particles (A) is carried out as a one-step polymerization or by a two-step polymerization method, after the emulsion polymerization is completed, by adding a neutralizing agent to the polymerization mixture, it is preferable to adjust the pH to about 4.5 to 10.5, preferably 5.0 to 10.0, more preferably 5.5 to 9.5. The neutralizing agent used here is not particularly limited, and examples thereof include metal hydroxides such as sodium hydroxide and potassium hydroxide; ammonia and the like. By setting the pH within the above range, the stability of the polymer particles (A) becomes good. After the neutralization treatment, by concentrating the polymerization mixture, the solid content concentration can be increased while maintaining the good stability of the polymer particles (A).

[0073] The timing of substituting the hydroxyl group of the repeating unit (a1) with a protecting group when synthesizing the polymer particles (A) may be simultaneous with the emulsion polymerization or after the emulsion polymerization is completed. However, since the operation is easy, it is preferably after the emulsion polymerization is completed. When provided after the emulsion polymerization is completed, it may be at any stage before or after adding the neutralizing agent, and a liquid medium in which the compound for introducing the protecting group dissolves may be appropriately added. The liquid medium is not particularly limited as long as it is a liquid medium capable of dissolving the compound for introducing the protecting group, but is preferably a non-aqueous medium. By adding the liquid medium, the introduction ratio of the compound for introducing the protecting group may be improved.

[0074] 1.1.4. Content ratio of polymer particles (A) The content ratio of the polymer particles (A) in the composition for an electric power storage device according to the present embodiment is preferably 10 to 100% by mass, more preferably 20 to 95% by mass, and particularly preferably 25 to 90% by mass in 100% by mass of the polymer component. Here, the polymer component includes the polymer particles (A), polymers other than the polymer particles (A) described later, thickeners, and the like.

[0075] 1.2. Liquid medium (B) The composition for an energy storage device according to this embodiment contains a liquid medium (B). The liquid medium (B) is preferably an aqueous medium containing water, and more preferably water. The aqueous medium can contain a non-aqueous medium other than water. Examples of this non-aqueous medium include amide compounds, hydrocarbons, alcohols, ketones, esters, amine compounds, lactones, sulfoxides, sulfone compounds, etc., and one or more selected from these can be used. By using an aqueous medium as the liquid medium (B), the composition for an energy storage device according to this embodiment has a low degree of adverse impact on the environment and also has high safety for the handling workers.

[0076] The content ratio of the non-aqueous medium contained in the aqueous medium is preferably 10% by mass or less, more preferably 5% by mass or less, and particularly preferably substantially not contained in 100% by mass of the aqueous medium. Here, "substantially not contained" means to the extent that the non-aqueous medium is not intentionally added as the liquid medium (B), and it may include non-aqueous media that are unavoidably mixed in when preparing the composition for an energy storage device.

[0077] 1.3. Other Additives The composition for an energy storage device according to this embodiment can contain additives other than the above-described components as necessary. Examples of such additives include polymers other than the polymer particles (A), preservatives, thickeners, etc.

[0078] 1.3.1. Polymers Other than Polymer Particles (A) The composition for an electric storage device according to this embodiment may contain a polymer other than the polymer particles (A). Such polymers are not particularly limited, and examples thereof include acrylic polymers containing unsaturated carboxylic acid esters or derivatives thereof as constituent units, fluorine-based polymers such as PVDF (polyvinylidene fluoride), and styrene-butadiene polymers (hereinafter also referred to as "SBR"). These polymers may be used alone or in combination of two or more. By containing these polymers, flexibility and adhesion may be further improved.

[0079] The content ratio of the polymer other than the polymer particles (A) in the composition for an electric storage device according to this embodiment is preferably 10 to 90% by mass, more preferably 20 to 80% by mass, and particularly preferably 25 to 75% by mass with respect to the total 100% by mass of the polymer particles (A), the polymer other than the polymer particles (A), and the thickener.

[0080] 1.3.2. Preservative The composition for an electric storage device according to this embodiment may contain a preservative. By containing a preservative, it may be possible to suppress the growth of bacteria, mold, etc. and the generation of foreign substances when the composition for an electric storage device is stored. Specific examples of the preservative include the compounds described in Japanese Patent No. 5477610.

[0081] 1.3.3. Thickener The composition for an electric storage device according to this embodiment may contain a thickener. By containing a thickener, the coating property of the slurry and the charge-discharge characteristics of the resulting electric storage device may be further improved.

[0082] Specific examples of the thickener include, for example, cellulose compounds such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose; poly(meth)acrylic acid; ammonium salts or alkali metal salts of the cellulose compound or the poly(meth)acrylic acid; polyvinyl alcohol-based (co)polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymer; and water-soluble polymers such as saponified products of copolymers of unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, and fumaric acid and vinyl esters. Among these, alkali metal salts of carboxymethyl cellulose, alkali metal salts of poly(meth)acrylic acid, etc. are preferable.

[0083] Examples of commercially available products of these thickeners include alkali metal salts of carboxymethyl cellulose such as CMC1120, CMC1150, CMC2200, CMC2280, and CMC2450 (all manufactured by Daicel Corporation).

[0084] When the composition for a power storage device according to this embodiment contains a thickener, the content ratio of the thickener is preferably 5% by mass or less, more preferably 0.1 to 4% by mass, based on 100% by mass of the total solid content of the composition for a power storage device.

[0085] 1.4. pH of the composition for a power storage device The pH of the composition for a power storage device according to this embodiment is preferably 4.5 to 10.5, more preferably 5.0 to 10.0, and particularly preferably 5.5 to 9.5. If the pH is within the above range, it is possible to suppress the occurrence of problems such as insufficient leveling property and liquid dripping, and it becomes easy to manufacture a power storage device electrode that achieves both good electrical characteristics and adhesion.

[0086] As used herein, "pH" refers to a physical property measured as follows. It is a value measured in accordance with JIS Z8802:2011 using a pH meter calibrated with neutral phosphate standard solution and borate standard solution as pH standard solutions at 25°C and using a glass electrode. Examples of such pH meters include "HM-7J" manufactured by Toa DKK Corporation and "D-51" manufactured by Horiba, Ltd.

[0087] Note that although it is not denied that the pH of the composition for a power storage device is affected by the monomer composition constituting the polymer particles (A), it is noted that it is not determined solely by the monomer composition. That is, generally, even with the same monomer composition, it is known that the pH of the composition for a power storage device changes depending on polymerization conditions and the like, and the examples in the present specification show only one example of this.

[0088] For example, even with the same monomer composition, when all unsaturated carboxylic acids are charged into the polymerization reaction solution from the beginning and then other monomers are sequentially added, and when monomers other than unsaturated carboxylic acids are charged into the polymerization reaction solution and finally unsaturated carboxylic acid is added, the amount of carboxy groups derived from unsaturated carboxylic acids exposed on the surface of the resulting polymer is different. It is considered that just changing the order of adding monomers in this way of polymerization method causes a large difference in the pH of the composition for a power storage device.

[0089] 2. Slurry for a power storage device electrode The slurry for a power storage device electrode according to an embodiment of the present invention contains the above-described composition for a power storage device and an active material. The above-described composition for a power storage device is used as a material for producing a power storage device electrode (active material layer) with improved binding ability between active materials, adhesion ability between the active material and the current collector, and resistance to powder falling. Hereinafter, the slurry for a power storage device electrode will be described in detail.

[0090] 2.1. Composition for a power storage device The composition for a power storage device has been described above, and thus the description thereof will be omitted.

[0091] The content ratio of the polymer component in the slurry for the electrode of the energy storage device according to the present embodiment is preferably 1 to 8 parts by mass, more preferably 1 to 7 parts by mass, and particularly preferably 1.5 to 6 parts by mass with respect to 100 parts by mass of the active material. When the content ratio of the polymer component is within the above range, the dispersibility of the active material in the slurry becomes good, and the coatability of the slurry is also excellent. Here, the polymer component includes polymer particles (A), polymers other than the polymer particles (A), a thickener, and the like.

[0092] 2.2. Active Material Examples of the active material used in the slurry for the electrode of the energy storage device according to the present embodiment include oxides containing lithium atoms, carbon materials, silicon materials, lead compounds, tin compounds, arsenic compounds, antimony compounds, aluminum compounds, conductive polymers such as polyacene, X A Y O Z (where A is an alkali metal or a transition metal, B is at least one selected from transition metals such as cobalt, nickel, aluminum, tin, manganese, etc., O represents an oxygen atom, and X, Y, and Z are numbers in the ranges of 1.10 > X > 0.05, 4.00 > Y > 0.85, and 5.00 > Z > 1.5, respectively) and composite metal oxides represented by the like, and other metal oxides. Specific examples thereof include the compounds described in Japanese Patent No. 5999399.

[0093] Examples of the oxide containing a lithium atom include one or more selected from lithium atom-containing oxides (olivine-type lithium-containing phosphate compounds) represented by the following general formula (1) and having an olivine-type crystal structure.

[0094] Li 1-x M x (AO4) ·····(1) (In formula (1), M is an ion of at least one metal selected from the group consisting of Mg, Ti, V, Nb, Ta, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga, Ge, and Sn; A is at least one selected from the group consisting of Si, S, P, and V; and x is a number satisfying the relationship 0 < x < 1.) Note that the value of x in the general formula (1) is selected so that the valence of the entire general formula (1) becomes 0 in accordance with the valences of M and A.

[0095] Examples of the olivine-type lithium-containing phosphate compound include LiFePO4, LiCoPO4, LiMnPO4, Li 0.90 Ti 0.05 Nb 0.05 Fe 0.30 Co 0.30 Mn 0.30 PO4 and the like. Among these, LiFePO4 (lithium iron phosphate) is particularly preferable because the iron compound used as a raw material is easily available and inexpensive.

[0096] The average particle diameter of the olivine-type lithium-containing phosphate compound is preferably in the range of 1 to 30 μm, more preferably in the range of 1 to 25 μm, and particularly preferably in the range of 1 to 20 μm.

[0097] Examples of the carbon material include amorphous carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), pitch-based carbon fibers, and the like.

[0098] Examples of the silicon material include elemental silicon, silicon oxide, silicon alloy, etc. In addition, for example, SiC, SiO x C y (0 < x ≤ 3, 0 < y ≤ 5), Si3N4, Si2N2O, SiO xSi oxide composites represented by (0 < x ≤ 2) (such as materials described in JP-A-2004-185810 and JP-A-2005-259697), and the silicon materials described in JP-A-2004-185810 can be used. Further, the silicon compounds containing a lithium compound and oxygen described in JP-A-2017-097952 can be used. As the silicon oxide, a silicon oxide represented by the compositional formula SiO x (0 < x < 2, preferably 0.1 ≤ x ≤ 1) is preferred. As the silicon alloy, an alloy of silicon and at least one transition metal selected from the group consisting of titanium, zirconium, nickel, copper, iron, and molybdenum is preferred. These transition metal silicon alloys are preferably used because they have high electron conductivity and high strength. Further, since the active material contains these transition metals, the transition metals present on the surface of the active material are oxidized to form an oxide having a hydroxyl group on the surface, which is also preferred in that the binding force with the binder becomes better. As the silicon alloy, it is more preferable to use a silicon-nickel alloy or a silicon-titanium alloy, and it is particularly preferable to use a silicon-titanium alloy. The content ratio of silicon in the silicon alloy is preferably 10 mol% or more, more preferably 20 to 70 mol%, based on all of the metal elements in the alloy. Note that the silicon material may be any of single crystal, polycrystal, and amorphous.

[0099] As the silicon compound containing the lithium compound and oxygen, a silicon compound (SiO x: Silicon compounds containing silicon compound particles (hereinafter also referred to as "lithium-silicon compound particles") containing (0.5 ≦ x ≦ 1.6) and crystalline Li2SiO3 are exemplified. Among the lithium silicates obtained by changing SiO2, the lithium-silicon compound particles have a large amount of Li2SiO3 that is stable against water, so the stability against the aqueous slurry used during electrode fabrication is improved, and the cycle characteristics of the power storage device are also improved, which is preferable. The lithium-silicon compound particles preferably have a median diameter of 1.0 μm or more and 15 μm or less. If the median diameter is 1.0 μm or more, the charge-discharge characteristics become good due to the increase in the surface area per unit mass. On the other hand, by setting the median diameter to 15 μm or less, it becomes difficult for the particles to crack, so it becomes difficult for a new surface to appear.

[0100] In addition, in the active material layer, conductive polymers such as polyacene; A X B Y O Z (However, A is an alkali metal or a transition metal, B is at least one selected from transition metals such as cobalt, nickel, aluminum, tin, manganese, etc., O represents an oxygen atom, and X, Y, and Z are numbers in the ranges of 1.10 > X > 0.05, 4.00 > Y > 0.85, and 5.00 > Z > 1.5, respectively), and composite metal oxides represented thereby, and other metal oxides, etc. may be included. Examples of the composite metal oxide include lithium cobaltate, lithium nickelate, lithium manganate, ternary lithium nickel cobalt manganate, etc.

[0101] The slurry for a power storage device electrode according to the present embodiment can be used when fabricating any of the positive and negative electrodes of the power storage device, but it is preferably used for both the positive and negative electrodes.

[0102] When a liquid medium mainly composed of water is used when fabricating the positive electrode slurry, there is a problem of inferior charge-discharge characteristics. It is known that the positive electrode active material has high reactivity with water, and it is considered that one of the factors is that the hydroxide ions generated by the reaction between the positive electrode active material and water corrode the positive electrode surface.

[0103] However, even when a liquid medium mainly composed of water is used as the liquid medium of the positive electrode slurry, the power storage device electrode produced using the slurry for the power storage device electrode according to this embodiment can exhibit good charge-discharge characteristics without causing the above-described problems. The reason for this is considered to be that the protecting group of the polymer particles (A) reacts with the hydroxide ions generated by the reaction between the positive electrode active material and water, and is deprotected, so that the hydroxide ions in the system are consumed and corrosion of the positive electrode surface can be suppressed.

[0104] On the other hand, when manufacturing the negative electrode, among the above-exemplified active materials, it is preferable to contain a silicon material. Since the silicon material has a larger lithium storage amount per unit weight compared to other active materials, by containing a silicon material as the negative electrode active material, the power storage capacity of the power storage device can be increased, and as a result, the output and energy density of the power storage device can be increased.

[0105] Moreover, among silicon materials, a silicon compound containing a lithium compound and oxygen is more preferable. The silicon material can react with lithium during charging to generate SiO2, which becomes an irreversible component. Therefore, by previously containing a lithium compound and oxygen in the silicon compound, the generation of the irreversible component can be suppressed, and the charge-discharge characteristics can be improved.

[0106] However, when using a silicon compound containing a lithium compound and oxygen as the negative electrode active material there is a problem that the adhesion is easily impaired when using a liquid medium mainly composed of water. The silicon compound containing a lithium compound and oxygen easily reacts with water to generate hydroxide ions, and it is considered that this hydroxide ion decomposes the thickener, which is one of the factors.

[0107] In addition, when the thickener is decomposed, the stress of the thickener coating the active material decreases, and it becomes impossible to follow the expansion and contraction of the active material. As a result, the electrode expansion increases, and the silicon compound (negative electrode active material) containing the lithium compound and oxygen becomes isolated, leading to a problem of deterioration in the charge-discharge characteristics of the power storage device.

[0108] The power storage device electrode produced using the slurry for a power storage device electrode according to this embodiment can exhibit good adhesion without causing the above-described problems even when a silicon compound containing a lithium compound and oxygen is used. The reason for this is considered to be that the protective group of the polymer particles (A) reacts with the hydroxide ions generated by the reaction between the negative electrode active material and water and is deprotected, thereby suppressing the decomposition of the thickener.

[0109] The content ratio of the silicon material in 100% by mass of the active material is preferably 1% by mass or more, more preferably 1 to 50% by mass, still more preferably 5 to 45% by mass, and particularly preferably 10 to 40% by mass. When the content ratio of the silicon material in 100% by mass of the active material is within the above range, a power storage device excellent in the balance between the output and energy density improvement of the power storage device and the charge-discharge durability characteristics can be obtained.

[0110] The shape of the active material is preferably particulate. The average particle diameter of the active material is preferably 0.1 to 100 μm, more preferably 1 to 20 μm. Here, the average particle diameter of the active material refers to the volume average particle diameter calculated from the particle size distribution measured using a particle size distribution measuring device based on the laser diffraction method as the measurement principle. Examples of such a laser diffraction type particle size distribution measuring device include the HORIBA LA-300 series and the HORIBA LA-920 series (both manufactured by Horiba, Ltd.).

[0111] The proportion of the use of the active material is preferably such that the content ratio of the polymer particles (A) to 100 parts by mass of the active material is 0.5 to 8 parts by mass, more preferably such that it is 1 to 7 parts by mass, and particularly preferably such that it is 1.5 to 6 parts by mass. By setting the proportion of use in this way, an electrode with excellent adhesion, small electrode resistance, and excellent charge-discharge characteristics can be manufactured.

[0112] 2.3. Other components In the slurry for a storage device electrode according to the present embodiment, other components may be added as necessary in addition to the components described above. Examples of such components include polymers other than the polymer particles (A), thickeners, liquid media, conductivity-imparting agents, pH adjusters, corrosion inhibitors, cellulose fibers, and the like. As the polymer other than the polymer particles (A) and the thickener, they can be appropriately selected from the compounds exemplified in the section of "1.3. Other additives" and used with the same purpose and content ratio.

[0113] <Liquid medium> In the slurry for a storage device electrode according to the present embodiment, in addition to the carry-over from the composition for a storage device, a liquid medium may be further added. The added liquid medium may be of the same type as or different from the liquid medium (B) contained in the composition for a storage device, but it is preferably selected from the liquid media exemplified in the section of "1.2. Liquid medium (B)" and used.

[0114] The content ratio of the liquid medium (including the carry-over from the composition for a storage device) in the slurry for a storage device electrode according to the present embodiment is preferably such that the solid content concentration in the slurry (which refers to the ratio of the total mass of the components other than the liquid medium in the slurry to the total mass of the slurry. The same applies hereinafter) is 30 to 70% by mass, and more preferably such that it is 40 to 60% by mass.

[0115] <Conductivity-imparting agent> In the slurry for the electrode of the energy storage device according to the present embodiment, a conductivity-imparting agent may be further added for the purpose of imparting conductivity and buffering the volume change of the active material due to the entry and exit of lithium ions.

[0116] Specific examples of the conductivity-imparting agent include carbons such as activated carbon, acetylene black, ketjen black, furnace black, graphite, carbon fiber, fullerene, and carbon nanotube. Among these, acetylene black or carbon nanotube can be preferably used. The content ratio of the conductivity-imparting agent is preferably 20 parts by mass or less, more preferably 1 to 15 parts by mass, and particularly preferably 2 to 10 parts by mass with respect to 100 parts by mass of the active material.

[0117] <pH adjuster·corrosion inhibitor> In the slurry for the electrode of the energy storage device according to the present embodiment, a pH adjuster or a corrosion inhibitor or both may be further added for the purpose of suppressing the corrosion of the current collector according to the type of the active material.

[0118] Examples of the pH adjuster include hydrochloric acid, phosphoric acid, sulfuric acid, acetic acid, formic acid, ammonium phosphate, ammonium sulfate, ammonium acetate, ammonium formate, ammonium chloride, sodium hydroxide, potassium hydroxide, etc. Among these, sulfuric acid, ammonium sulfate, sodium hydroxide, and potassium hydroxide are preferable. It can also be selected and used from among the neutralizing agents described in the method for producing the polymer particles (A).

[0119] Examples of the corrosion inhibitor include ammonium metavanadate, sodium metavanadate, potassium metavanadate, ammonium metatungstate, sodium metatungstate, potassium metatungstate, ammonium paratungstate, sodium paratungstate, potassium paratungstate, ammonium molybdate, sodium molybdate, potassium molybdate, etc. Among these, ammonium paratungstate, ammonium metavanadate, sodium metavanadate, potassium metavanadate, and ammonium molybdate are preferable.

[0120] <Cellulose fiber> Cellulose fibers may be further added to the slurry for the power storage device electrode according to this embodiment. Adding cellulose fibers may improve the adhesion of the active material to the current collector. It is considered that the fibrous cellulose fibers can prevent the active material from falling off and improve the adhesion to the current collector by fiber-bonding or fiber-contact adjacent active materials in a fibrous form.

[0121] The average fiber length of the cellulose fibers can be selected from a wide range of 0.1 to 1000 μm. For example, it is preferably 1 to 750 μm, more preferably 1.3 to 500 μm, still more preferably 1.4 to 250 μm, and particularly preferably 1.8 to 25 μm. If the average fiber length is within the above range, the surface smoothness (coating uniformity) may be good, and the adhesion of the active material to the current collector may be improved.

[0122] The fiber length of the cellulose fibers may be uniform, and the coefficient of variation of the fiber length ([standard deviation of fiber length / average fiber length] × 100) is, for example, preferably 0.1 to 100, more preferably 0.5 to 50, and particularly preferably 1 to 30. The maximum fiber length of the cellulose fibers is, for example, preferably 500 μm or less, more preferably 300 μm or less, still more preferably 200 μm or less, even more preferably 100 μm or less, and particularly preferably 50 μm or less.

[0123] When the average fiber length of the cellulose fiber is set to 5 times or less the average thickness of the active material layer, it is advantageous because the surface smoothness (coating film uniformity) and the adhesion of the active material to the current collector are further improved. The average fiber length of the cellulose fiber is preferably 0.01 to 5 times, more preferably 0.02 to 3 times, and particularly preferably 0.03 to 2 times the average thickness of the active material layer.

[0124] The average fiber diameter of the cellulose fiber is preferably 1 nm to 10 μm, more preferably 5 nm to 2.5 μm, still more preferably 20 nm to 700 nm, and particularly preferably 30 nm to 200 nm. When the average fiber diameter is within the above range, the occupied volume of the fiber does not become too large, and the packing density of the active material may be increased. Therefore, the cellulose fiber is preferably a cellulose nanofiber having a nanometer-sized average fiber diameter (for example, a cellulose nanofiber having an average fiber diameter of 10 nm to 500 nm, preferably about 25 nm to 250 nm).

[0125] The fiber diameter of the cellulose fiber is also uniform, and the coefficient of variation of the fiber diameter ([standard deviation of fiber diameter / average fiber diameter] × 100) is preferably 1 to 80, more preferably 5 to 60, and particularly preferably 10 to 50. The maximum fiber diameter of the cellulose fiber is preferably 30 μm or less, more preferably 5 μm or less, and particularly preferably 1 μm or less.

[0126] The ratio (aspect ratio) of the average fiber length to the average fiber diameter of the cellulose fiber is, for example, preferably 10 to 5000, more preferably 20 to 3000, and particularly preferably 50 to 2000. When the aspect ratio is within the above range, the adhesion of the active material to the current collector is good, and the surface smoothness (coating film uniformity) of the electrode may be good without weakening the breaking strength of the fiber.

[0127] In the present invention, the average fiber length, the standard deviation of the fiber length distribution, the maximum fiber length, the average fiber diameter, the standard deviation of the fiber diameter distribution, and the maximum fiber diameter may be values calculated from fibers (about n = 20) measured based on an electron micrograph.

[0128] The material of the cellulose fiber only needs to be formed of a polysaccharide having a β-1,4-glucan structure. Examples of the cellulose fiber include cellulose fibers derived from higher plants (e.g., cellulose fibers derived from wood (such as wood pulp from coniferous trees, broad-leaved trees, etc.), bamboo fibers, sugarcane fibers, seed hair fibers (e.g., cotton linter, bombax cotton, kapok, etc.), bast fibers (e.g., hemp, kozo, mitsumata, etc.), leaf fibers (e.g., manila hemp, New Zealand hemp, etc.), etc., such as natural cellulose fibers (pulp fibers)), cellulose fibers derived from animals (e.g., sea squirt cellulose, etc.), cellulose fibers derived from bacteria (e.g., cellulose contained in nata de coco, etc.), and chemically synthesized cellulose fibers (e.g., rayon, cellulose esters (such as cellulose acetate), cellulose ethers (e.g., hydroxyalkyl celluloses such as hydroxyethyl cellulose (HEC), hydroxypropyl cellulose, alkyl celluloses such as methyl cellulose, ethyl cellulose, etc., such as cellulose derivatives)). These cellulose fibers may be used alone or in combination of two or more.

[0129] Among these cellulose fibers, cellulose fibers derived from pulp, such as cellulose fibers derived from higher plants (e.g., wood fibers (such as wood pulp from coniferous trees, broad-leaved trees, etc.) and seed hair fibers (such as cotton linter pulp)), are preferred because it is easy to prepare nanofibers having an appropriate aspect ratio.

[0130] The method for producing the cellulose fiber is not particularly limited, and a conventional method, for example, the methods described in Japanese Patent Publication No. 60-19921, Japanese Patent Application Laid-Open No. 2011-26760, Japanese Patent Application Laid-Open No. 2012-25833, Japanese Patent Application Laid-Open No. 2012-36517, Japanese Patent Application Laid-Open No. 2012-36518, Japanese Patent Application Laid-Open No. 2014-181421, etc., may be used according to the target fiber length and fiber diameter.

[0131] 2.4. Method for Preparing Slurry for Electrodes of Energy Storage Devices The slurry for a power storage device electrode according to the present embodiment may be manufactured by any method as long as it contains the above-described composition for a power storage device and the active material. From the viewpoint of manufacturing a slurry having better dispersibility and stability more efficiently and inexpensively, it is preferable to add the active material and optional components used as necessary to the composition for a power storage device and mix them. Specific manufacturing methods include, for example, the methods described in Japanese Patent No. 6544150.

[0132] 3. Power storage device electrode A power storage device electrode according to an embodiment of the present invention includes a current collector and an active material layer formed by applying and drying the above-described slurry for a power storage device electrode on the surface of the current collector. Such a power storage device electrode can be manufactured by applying the above-described slurry for a power storage device electrode on the surface of a current collector such as a metal foil to form a coating film, and then drying the coating film to form an active material layer. The power storage device electrode manufactured in this way has an active material layer containing the above-described polymer particles (A), the active material, and optional components added as necessary bound to the surface of the current collector. Therefore, the occurrence of corrosion on the electrode surface is suppressed, the adhesion is excellent, and the charge-discharge durability characteristics of the power storage device can be improved.

[0133] The current collector is not particularly limited as long as it is made of a conductive material. When the power storage device electrode is used in a lithium-ion secondary battery, for example, a current collector made of a metal such as iron, copper, aluminum, nickel, or stainless steel can be used. In particular, an aluminum or copper current collector is preferable.

[0134] When the power storage device electrode is used in a nickel-metal hydride secondary battery, for example, a current collector made of punched metal, expanded metal, wire mesh, foamed metal, sintered body of reticulated metal fibers, metal-plated resin plate, or the like can be used.

[0135] The shape and thickness of the current collector are not particularly limited. For example, a sheet-like current collector with a thickness of about 0.001 to 0.5 mm is preferred. When applying the slurry for the electrode of the power storage device to the surface of the current collector, the application method is not particularly limited. As the application method, for example, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, an immersion method, a brush coating method, etc. can be appropriately used.

[0136] The coating amount of the slurry for the electrode of the power storage device is not particularly limited. A coating amount that results in a thickness of the positive electrode active material layer of 0.005 to 5 mm after applying the slurry for the electrode of the power storage device and removing the liquid medium (a concept including both water and an optionally used non-aqueous medium) is preferred, and a coating amount that results in a thickness of 0.01 to 2 mm is more preferred.

[0137] When the thickness of the active material layer is within the above range, the electrolyte can efficiently penetrate into the active material layer. As a result, the transfer of metal ions accompanying charge and discharge between the active material and the electrolyte in the active material layer can be easily carried out, so that the internal resistance of the electrode can be further reduced.

[0138] Also, when the thickness of the active material layer is within the above range, even when the electrode is processed by folding, winding, etc., the adhesion between the active material layer and the current collector is good, and the active material layer is difficult to peel off from the current collector. That is, it is also preferable in that a power storage device electrode rich in flexibility can be easily obtained.

[0139] The drying method of the coating film formed by applying the slurry for the electrode of the power storage device (the method for removing water and an optionally used non-aqueous medium) is not particularly limited. For example, drying with warm air, hot air, low humidity air; vacuum drying; drying by irradiation with (far) infrared rays, electron beams, etc. can be used.

[0140] When drying a coating film formed by applying a slurry for an electrode of an energy storage device, the drying rate can be appropriately set so that the liquid medium can be removed as quickly as possible under conditions such as no cracks in the active material layer due to stress concentration and no peeling of the active material layer from the current collector.

[0141] After drying the coating film formed by applying the slurry for the electrode of the energy storage device, it is preferable to press the electrode of the energy storage device to increase the density of the active material layer and adjust the density and porosity in the active material layer to the ranges shown below.

[0142] The density of the active material layer after pressing is preferably 1.1 to 2.1 g / cm 3 for the negative electrode, more preferably 1.2 to 2.0 g / cm 3 even more preferably 1.3 to 1.8 g / cm 3 still more preferably 1.4 to 1.7 g / cm 3 and particularly preferably 1.4 to 1.7 g / cm. For the positive electrode, it is preferably 2.5 to 3.5 g / cm 3 more preferably 2.6 to 3.4 g / cm 3 even more preferably 2.7 to 3.3 g / cm 3 still more preferably 2.8 to 3.2 g / cm 3 and particularly preferably 2.8 to 3.2 g / cm. If the density of the active material layer is within the above range, an electrode for an energy storage device with good adhesion between the current collector and the active material layer, excellent powder falling property, and excellent electrical characteristics can be obtained.

[0143] The porosity of the active material layer after pressing is preferably 10 to 50%, more preferably 15 to 45%, and particularly preferably 20 to 40%. If the porosity of the active material layer is within the above range, an electrode for an energy storage device with good adhesion between the current collector and the active material layer, excellent powder falling property, and excellent electrical characteristics can be obtained.

[0144] Moreover, if the porosity of the active material layer is within the above range, the electrolyte can be sufficiently impregnated into the active material layer, and the active material surface and the electrolyte can be sufficiently contacted. As a result, the transfer of lithium ions between the active material and the electrolyte becomes easy, and good charge and discharge characteristics can be exhibited.

[0145] Examples of the pressing method include methods such as die pressing and roll pressing. The pressing conditions can be appropriately set according to the type of pressing equipment used, the desired values of the porosity and density of the active material layer, etc. The pressing conditions can be easily set by a few preliminary experiments by those skilled in the art.

[0146] When using the roll pressing method, the pressing conditions can be, for example, as follows. · Linear pressure of the roll press: 0.1 to 10 (t / cm), preferably 0.5 to 5 (t / cm). · Roll temperature: 20 to 100 °C. · Feed rate of the energy storage device electrode (rotation speed of the roll): 0.5 to 50 m / min, preferably or 1 to 30 m / min.

[0147] 4. Energy storage device The energy storage device according to an embodiment of the present invention includes the above-described energy storage device electrode, further contains an electrolyte, and can be manufactured according to a conventional method using components such as a separator. Specific manufacturing methods include, for example, a method of stacking a negative electrode and a positive electrode via a separator, winding, folding, etc. according to the battery shape, storing them in a battery container, injecting an electrolyte into the battery container, and sealing it. The shape of the battery can be an appropriate shape such as a coin type, a cylindrical type, a rectangular type, a laminate type, etc.

[0148] The electrolyte may be in a liquid state or a gel state, and depending on the type of active material, one that effectively exhibits the function as a battery may be selected from known electrolytes used in energy storage devices. The electrolyte can be a solution in which an electrolyte is dissolved in a suitable solvent. Examples of such electrolytes and solvents include the compounds described in, for example, Japanese Patent No. 5999399.

[0149] The above-described energy storage device is applicable to a lithium-ion secondary battery, an electric double layer capacitor, a lithium-ion capacitor, etc. that require discharge at a high current density. Among these, a lithium-ion secondary battery is particularly preferred. In the energy storage device electrode and the energy storage device according to this embodiment, members other than the energy storage device composition can use known members for lithium-ion secondary batteries, electric double layer capacitors, or lithium-ion capacitors.

[0150] 5. Examples Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. "Parts" and "%" in the examples and comparative examples are based on mass unless otherwise specified. In this specification, the polymer particles (A) produced in Example 1 are referred to as "polymer particles (A-1)", and similarly, the polymer particles (A) produced in Example 2 are referred to as "polymer particles (A-2)", etc.

[0151] 5.1. Example 1 5.1.1. Production and Physical Property Evaluation of Polymer Particles (A) 5.1.1.1. Production of Polymer Particles (A) A separable flask with a capacity of 7 liters was charged with 150 parts by mass of water and 0.2 part by mass of sodium dodecylbenzenesulfonate, and the inside of the separable flask was thoroughly purged with nitrogen. On the other hand, in another container, 60 parts by mass of water, 0.8 part by mass of an ether sulfate type emulsifier (trade name "Adekaria Soap SR1025", manufactured by ADEKA CORPORATION) as a solid content, 10 parts by mass of cyclohexyl methacrylate (CHMA) as a monomer, 2 parts by mass of acrylonitrile (AN), 30 parts by mass of 2-ethylhexyl acrylate (EHA), 30 parts by mass of 2-hydroxyethyl methacrylate (HEMA), 10 parts by mass of methyl methacrylate (MMA), 5 parts by mass of allyl methacrylate (AMA), 9 parts by mass of styrene (ST), 1 part by mass of divinylbenzene (DVB) and 3 parts by mass of acrylic acid (AA) were added, and the mixture was thoroughly stirred to prepare a monomer emulsion containing the above monomer mixture. The temperature rise inside the separable flask was started, and when the internal temperature reached 60 °C, 0.5 part by mass of ammonium persulfate was added as a polymerization initiator. Then, when the internal temperature of the separable flask reached 70 °C, the addition of the monomer emulsion prepared above was started, and the monomer emulsion was slowly added over 3 hours while maintaining the internal temperature of the separable flask at 70 °C. Thereafter, the internal temperature of the separable flask was raised to 85 °C, and this temperature was maintained for 3 hours to carry out a polymerization reaction. After 3 hours, the separable flask was cooled to stop the reaction, and then aqueous ammonia was added to adjust the pH to 8.0, thereby obtaining an aqueous dispersion containing 40% by mass of polymer particles. Next, the acylating agent shown in Table 1 was charged and reacted at 80 °C for 4 hours to obtain an aqueous dispersion containing polymer particles (A-1) in which a part of the hydroxyl groups of the polymer particles were substituted with acyl groups. Thereafter, the residual monomer was treated by steam distillation and concentrated under reduced pressure to 50% by mass of the solid content to obtain an aqueous dispersion containing 50% by mass of polymer particles (A-1).

[0152] 5.1.1.2. Physical Property Evaluation of Polymer Particles (A) ​The polymer particles (A-1) obtained above were evaluated for pH, number-average particle diameter, surface acid amount, and swelling ratio. The results are shown in Table 1.

[0153] <Measurement of pH> Regarding the aqueous dispersion of the polymer (A-1) obtained above, when the pH at 25 °C was measured using a pH meter (manufactured by Horiba, Ltd.), it was confirmed that the pH was 8.0.

[0154] <Measurement of number-average particle diameter> A latex obtained by diluting the aqueous dispersion of the polymer particles (A-1) obtained above to 0.1 wt% was dropped onto a collodion support film drop by drop with a pipette, and further, a 0.02 wt% osmium tetroxide solution was dropped onto the collodion support film drop by drop with a pipette and air-dried for 12 hours to prepare a sample. The sample thus prepared was observed at a magnification of 10K using a transmission electron microscope (TEM, manufactured by Hitachi High-Technologies Corporation, model number "H-7650"), and image analysis was performed using the program of HITACHI EMIP to calculate the number-average particle diameter of 50 randomly selected polymer particles (A-1).

[0155] <Measurement of surface acid amount> The surface acid amount of the polymer particles (A-1) obtained above was measured as follows. First, it was confirmed that the burette of the potentiometric titration apparatus (manufactured by Kyoto Electronics Industry Co., Ltd., model "AT-510") and the reagent bottle at the upper part of the main body were filled with 0.005 mol / L sulfuric acid, and it was confirmed that the conductivity of ultrapure water was 2 μS or less. Next, for degassing the air in the burette, purging was performed, and further, the bubbles at the nozzle were removed. Then, an aqueous dispersion of the polymer particles (A-1) obtained above was sampled in a 300 mL beaker at about 1 g in terms of solid content, and the sample weight was recorded. After adding ultrapure water thereto and diluting to 200 mL, 1 mol / L aqueous sodium hydroxide solution was added dropwise. When the end point was reached, it was stirred for about 30 seconds, and it was confirmed that the conductivity had settled down. The RESET button of the measurement program was pressed to set it to the measurement standby state. The START button of the measurement program was pressed to start the measurement with 0.005 mol / L sulfuric acid. Since it automatically ends and the file is saved when the end point is reached, the obtained curve was analyzed, and the surface acid amount was determined from the following formula based on the amount of sulfuric acid used. Surface acid amount (mmol / g) = Amount of acid used [mL] in the carboxylic acid region on the particle surface × Concentration of acid [mol / L] × Degree of ionization / Sample weight [g] / 1000

[0156] <Measurement of swelling ratio> The polymer particles (A-1) obtained above were dried in a thermostatic bath at 85 °C for 24 hours to prepare a film. 1 g of this film was immersed in 20 mL of a mixed solution composed of propylene carbonate (PC) and diethyl carbonate (DEC) (PC / DEC = 1 / 1 (volume ratio), hereinafter this mixed solution is referred to as "PC / DEC"), and shaken at 70 °C for 24 hours. Next, it was filtered through a 300-mesh wire mesh to separate the insoluble matter, and then the weight (Y (g)) of the residue obtained by evaporating and removing PC / DEC of the dissolved matter was measured. Also, after absorbing and removing the PC / DEC adhering to the surface of the insoluble matter (film) separated by the above filtration with paper, the weight (Z (g)) of the insoluble matter (film) was measured. The swelling ratio of the polymer particles (A-1) was determined by the following formula. Swelling ratio (mass %) = (Z / (1 - Y)) × 100

[0157] <Degree of substitution of hydroxyl group> The acyl group substitution rate of the hydroxyl groups possessed by the polymer particles (A-1) was calculated as shown in formula (ii) using formula (i). [Number] Acyl group substitution rate (%) = (TSC a - TSC b ) / (X - TSC b ) × 100…(ii) (Explanation of symbols in formula (i) and formula (ii)) ·Solid content concentration (%) of the aqueous solution of polymer particles (A-1) before acylation: TSC b ·Solid content concentration (%) of the aqueous solution of polymer particles (A-1) after acylation: TSC a ·Number of parts by mass of the repeating unit (a1): w a1 ·Molecular weight of the repeating unit (a1): M a1 ·Increment in the molecular weight of the repeating unit (a1) before and after introduction of the acyl group: PG ·Number of hydroxyl groups per molecule of the repeating unit (a1): OH a1

[0158] 5.1.2. Preparation and Physical Property Evaluation of Slurry for Positive Electrode of Energy Storage Device 5.1.2.1. Preparation of Slurry for Positive Electrode of Energy Storage Device Into a twin-screw planetary mixer (manufactured by Primix Corporation, trade name "TK High Visc Mix 2P-03"), 2 parts by mass of the polymer particles (A-1) (in terms of solid content, added as the latex of the polymer particles (A-1) obtained above), 100 parts by mass of NMC622 (trade name "ME-8A", manufactured by Beijing Easpring Material Technology Co., Ltd.) as the positive electrode active material, 5 parts by mass of acetylene black, 2 parts by mass of a thickener (trade name "CMC2200", manufactured by Daicel Corporation), and 20 parts by mass of water were charged, and stirring was carried out at 60 rpm for 1 hour. Note that the NMC622 is an example of a positive electrode active material.

[0159] After that, the mixture was further stirred for 1 hour to obtain a paste. Water was added to the obtained paste to adjust the solid content to 70%, and then the mixture was stirred at 200 rpm for 2 minutes, at 1800 rpm for 5 minutes, and then further stirred under vacuum (approximately 5.0 × 10 3 The mixture was stirred and mixed at 1800 rpm for 1.5 minutes at 1000 kPa (200 psi) to prepare a slurry for a positive electrode of an electricity storage device.

[0160] 5.1.2.2. Evaluation of pH of Slurry for Positive Electrodes of Energy Storage Devices The slurry for the positive electrode of an electricity storage device obtained above was left to stand for 4 days at 25°C. The pH at 25°C was measured using a pH meter (manufactured by Horiba, Ltd.) after 1 day and 4 days, and was found to be 9.0 and 9.6, respectively. The evaluation results are shown in Table 1 below.

[0161] 5.1.3. Preparation and evaluation of positive electrodes for energy storage devices 5.1.3.1. Preparation of positive electrodes for energy storage devices The slurry for the positive electrode of an electricity storage device obtained above was uniformly applied to the surface of a current collector made of aluminum foil with a thickness of 20 μm by a doctor blade method so that the film thickness after drying would be 100 μm, and then dried at 120° C. for 20 minutes. After that, the density of the formed film (positive electrode active material layer) was 3.0 g / cm 3 The resultant was pressed using a roll press machine so as to obtain a positive electrode for an electricity storage device.

[0162] 5.1.3.2. Evaluation of Adhesion Strength On the surface of the obtained positive electrode for an electricity storage device, a knife was used to cut the active material layer to reach the current collector. Ten cuts were made in each direction at 2 mm intervals to a depth of 10 mm each, creating a grid pattern. 18 mm wide adhesive tape (manufactured by Nichiban Co., Ltd., product name "Cellotape" (registered trademark), specified in JIS Z1522) was applied to the cuts and immediately peeled off, and the degree of active material loss was evaluated visually. The evaluation criteria were as follows. The evaluation results are shown in Table 1 below. (Evaluation criteria) · 5 points: The number of shedding of the active material layer is 0. · 4 points: The number of shedding of the active material layer is 1 - 5. · 3 points: The number of shedding of the active material layer is 6 - 20. · 2 points: The number of shedding of the active material layer is 21 - 40. · 1 point: The number of shedding of the active material layer is 41 or more.

[0163] 5.1.4. Fabrication and Evaluation of the Energy Storage Device 5.1.4.1. Preparation of the Slurry for the Negative Electrode of the Energy Storage Device Into a biaxial planetary mixer (manufactured by Primix Corporation, trade name "TK Hibiscus Mix 2P-03"), 1 part by mass (in terms of solid content) of a thickener (trade name "CMC2200", manufactured by Daicel Corporation), 100 parts by mass (in terms of solid content) of graphite as the negative electrode active material, and 68 parts by mass of water were charged, and stirring was carried out at 60 rpm for 1 hour.

[0164] Next, an amount corresponding to 2 parts by mass (in terms of solid content) of SBR (trade name "TRD105A", manufactured by JSR Corporation) was added, and stirring was carried out for another 1 hour to obtain a paste. Water was added to the obtained paste, and after adjusting the solid content to 50%, using a stirring and defoaming machine (manufactured by Shin-Kee Co., Ltd., trade name "Awa Torineri"), stirring and mixing were carried out at 200 rpm for 2 minutes, 1800 rpm for 5 minutes, and further at 1800 rpm for 1.5 minutes under vacuum to prepare the slurry for the negative electrode of the energy storage device.

[0165] 5.1.4.2. Fabrication of the Negative Electrode for the Energy Storage Device On the surface of a current collector made of a copper foil with a thickness of 20 μm, the slurry for the negative electrode of the energy storage device obtained above was uniformly coated by the doctor blade method so that the film thickness after drying would be 80 μm, and drying treatment was carried out at 120 °C for 20 minutes. Then, so that the density of the formed film (negative electrode active material layer) would be 1.9 g / cm 3 the negative electrode for the energy storage device was obtained by pressing using a roll press machine.

[0166] 5.1.4.3. Assembly of the Lithium-Ion Battery Cell In a glove box replaced with Ar so that the dew point is -80°C or lower, the negative electrode for the power storage device manufactured above was punched and formed into a circle with a diameter of 15.95 mm and placed on a two-pole coin cell (manufactured by Takahata Co., Ltd., product name "HS Flat Cell").

[0167] Next, a separator made of a porous polypropylene film punched into a circle with a diameter of 24 mm (manufactured by Celgard LLC, product name "Celgard #2400") was placed. Further, after injecting 500 μL of electrolyte so that air does not enter, the positive electrode for the power storage device manufactured above, which was punched and formed into a circle with a diameter of 16.16 mm, was overlapped and placed on the separator, and the outer body of the two-pole coin cell was closed and sealed with a screw to assemble a lithium-ion battery cell (an example of a power storage device). The electrolyte used here is a solution in which LiPF6 is dissolved at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1 / 1 (mass ratio).

[0168] 5.1.4.4. Evaluation of cycle characteristics of lithium-ion battery Regarding the lithium-ion battery manufactured above, in a thermostat adjusted to 25°C, charging was started at a constant current (1.0C), and when the voltage reached 4.2V, charging was continued at a constant voltage (4.2V ) until the current value reached 0.01C, at which point charging was completed (cut-off). Then, discharging was started at a constant current (1.0C), and when the voltage reached 3.0V, discharging was completed (cut-off), and the discharge capacity of the first cycle was calculated. In this way, 100 charge-discharge cycles were repeated. The capacity retention rate was calculated by the following formula and evaluated according to the following criteria. The evaluation results are shown in Table 1 below. Capacity retention rate (%) = (Discharge capacity of the 100th cycle) / (Discharge capacity of the first cycle) (Evaluation criteria) · 5 points: Capacity retention rate is 95% or more. · 4 points: Capacity retention rate is 90% or more and less than 95%. · 3 points: Capacity retention rate is 85% or more and less than 90%. · 2 points: Capacity retention rate is 80% or more and less than 85%. ·1 point: The capacity retention rate is 75% or more and less than 80%. ·0 point: The capacity retention rate is less than 75%.

[0169] 5.2. Examples 2 to 10, Comparative Examples 1 to 5 In the section of "5.1.1.1. Production of Polymer Particles (A)", except that the types and amounts of the monomer and the acylating agent were the same as those described in Table 1 below, aqueous dispersions containing 50% of polymer particles (A) were obtained in the same manner. Except for using the aqueous dispersions of the polymer particles thus obtained, in the same manner as in Example 1, slurries for positive electrodes of power storage devices, positive and negative electrodes for power storage devices, and lithium-ion batteries were produced and evaluated in the same manner as in Example 1.

[0170] 5.3. Example 11 In the same manner as in Example 3, an aqueous dispersion with a pH of 8.0 containing 50% by mass of polymer particles (A-3) was obtained. Next, except that 2 parts by mass of a thickener (trade name "CMC2200", manufactured by Daicel Corporation) (in terms of solid content, added as an aqueous solution with a concentration of 2% by mass) and 4 parts by mass of polymer particles (A-3) (in terms of solid content, added as an aqueous dispersion with a pH of 8.0 containing 50% by mass of the polymer particles (A-3) obtained above) were changed, a slurry for a positive electrode of a power storage device was prepared in the same manner as in Example 1.

[0171] Except for using the slurry for a positive electrode of a power storage device prepared above, in the same manner as in Example 1, positive and negative electrodes for a power storage device and a lithium-ion battery were produced and evaluated in the same manner as in Example 1.

[0172] 5.4. Examples 12 to 21 Except that the composition of the slurry for a positive electrode of a power storage device was changed as shown in Table 2 below, slurries for a positive electrode of a power storage device were prepared in the same manner as in Example 11, positive and negative electrodes for a power storage device and a lithium-ion battery were produced in the same manner, and evaluated in the same manner as in Example 11.

[0173] 5.5. Example 22 5.5.1. Preparation and Physical Property Evaluation of Slurry for Negative Electrode of Power Storage Device In the same manner as in Example 1, an aqueous dispersion having a pH of 8.0 and containing 50% by mass of polymer particles (A-1) was obtained. Next, into a twin-screw planetary mixer (manufactured by Primix Corporation, trade name "TK Hibiscus Mix 2P-03"), 2 parts by mass of a thickener (trade name "CMC2200", manufactured by Daicel Corporation) (added as an aqueous solution with a solid content conversion value and a concentration of 2% by mass), 2 parts by mass of polymer particles (A-1) (added as an aqueous dispersion having a pH of 8.0 and containing 50% by mass of the polymer particles (A-1) obtained above in terms of solid content conversion value), a lithium compound and a silicon compound containing oxygen prepared by the method described in JP-A-2017-097952 as a negative electrode active material and a carbon-based active material were mixed at a mass ratio of 1:9 (here, as the carbon-based active material, a mixture of natural graphite and artificial graphite coated with a pitch layer at a mass ratio of 5:5 was used.) 100 parts by mass, 5 parts by mass of acetylene black, and 68 parts by mass of water were charged, and stirring was carried out at 600 rpm for 1 hour.

[0174] Thereafter, stirring was continued for another 1 hour to obtain a paste. After adding water to the obtained paste to adjust the solid content concentration to 50%, using a stirring and defoaming machine (manufactured by Shin-Kee Co., Ltd., trade name "Awa Tori Rentaro"), stirring was carried out at 200 rpm for 2 minutes, at 1800 rpm for 5 minutes, and further under vacuum (about 5.0×10 3 Pa) at 1800 rpm for 1.5 minutes to prepare a slurry for a negative electrode of an electric storage device.

[0175] 5.5.2. Evaluation of the pH of the slurry for a negative electrode of an electric storage device The slurry for a negative electrode of an electric storage device obtained above was left standing at 25°C for 1 day. When the pH at 25°C after 1 day was measured with a pH meter (manufactured by Horiba, Ltd.), it was 10.6. The evaluation results are shown in Table 3.

[0176] 5.5.3. Fabrication and evaluation of a negative electrode for an electric storage device 5.5.3.1. Fabrication of a negative electrode for an electric storage device On the surface of a current collector made of a copper foil with a thickness of 20 μm, the slurry for the negative electrode of the power storage device obtained above was uniformly applied by the doctor blade method so that the film thickness after drying would be 80 μm, and then dried at 120°C for 20 minutes. Then, the density of the formed film (negative electrode active material layer) was 1.9 g / cm 3 The negative electrode for the power storage device was obtained by pressing using a roll press so as to achieve.

[0177] 5.5.3.2. Evaluation of Adhesion Strength Evaluation was carried out in the same manner as the method described in "5.1.3.2. Evaluation of Adhesion Strength" except that the negative electrode for the power storage device obtained above was used.

[0178] 5.5.4. Fabrication and Evaluation of Power Storage Device A slurry for the positive electrode of the power storage device was prepared in the same manner as in Example 1, and a positive electrode for the power storage device was fabricated. A lithium-ion battery was fabricated in the same manner as in Example 1 except that the positive electrode for the power storage device thus obtained and the negative electrode for the power storage device obtained above were used, and evaluation was carried out in the same manner as in Example 1.

[0179] 5.6. Examples 23 to 31, Comparative Examples 6 to 10 Slurries for the negative electrodes of the power storage devices were respectively prepared in the same manner as in Example 22 except that the types of polymers added to the slurries for the negative electrodes of the power storage devices were changed as shown in Table 3 below. Positive and negative electrodes for the power storage devices and lithium-ion batteries were respectively fabricated, and evaluation was carried out in the same manner as in Example 22.

[0180] 5.7. Example 32 An aqueous dispersion with a pH of 8.0 containing 50% by mass of polymer particles (A-4) was obtained in the same manner as in Example 4. Next, a slurry for the negative electrode of the power storage device was prepared in the same manner as in Example 22 except that 2 parts by mass of a thickener (trade name "CMC2200", manufactured by Daicel Corporation) (added as an aqueous solution with a solid content conversion value and a concentration of 2% by mass) and 4 parts by mass of polymer particles (A-4) (added as an aqueous dispersion with a pH of 8.0 containing 50% by mass of the polymer particles (A-4) obtained above) were changed.

[0181] A power storage device negative electrode slurry prepared as described above was used, and power storage device positive and negative electrodes and lithium-ion batteries were produced in the same manner as in Example 22 and evaluated in the same manner as in Example 22.

[0182] 5.8. Examples 33 to 38 Except that the composition of the power storage device negative electrode slurry was changed as shown in Table 4 below, the power storage device negative electrode slurries were each prepared in the same manner as in Example 22. Power storage device positive and negative electrodes and lithium-ion batteries were produced, respectively, and evaluated in the same manner as in Example 22.

[0183] 5.9. Evaluation Results Tables 1 to 4 below show the polymer compositions used in Examples 1 to 38 and Comparative Examples 1 to 10, and the evaluation results. The numerical values representing the polymer compositions shown in Table 1 below represent mass %, and the numerical values representing the compositions shown in Tables 2 and 4 below represent parts by mass.

[0184]

Table 1

[0185]

Table 2

[0186]

Table 3

[0187]

Table 4

[0188] The abbreviations of the respective components in Tables 1 to 4 above represent the following compounds or trade names, respectively. <Unsaturated carboxylic acid ester having a hydroxyl group> ·HEMA: 2-Hydroxyethyl methacrylate ·HEA: 2-Hydroxyethyl acrylate ·GLM: Glycerin monomethacrylate <Unsaturated carboxylic acid ester> ·MMA: Methyl methacrylate ·CHMA: Cyclohexyl methacrylate ·2EHA: 2-Ethylhexyl acrylate ·BA: Butyl acrylate ·EA: Ethyl acrylate ·AMA: Allyl acrylate <Unsaturated carboxylic acid> ·TA: Itaconic acid ·AA: Acrylic acid ·MAA: Methacrylic acid <Aromatic vinyl compound> ·ST: Styrene ·DVB: Divinylbenzene <(Meth)acrylamide> ·AAM: Acrylamide ·MAM: Methacrylamide <α,β-unsaturated nitrile compound> ·AN: Acrylonitrile <Compound having a sulfonic acid group> ·NASS: Sodium styrene sulfonate <Acylating agent> ·A: Acetic anhydride ·B: Benzoyl chloride ·P: Pivaloyl chloride <Thickener> ·CMC: Trade name "CMC2200", manufactured by Daicel Corporation ·Alginic acid: Trade name "Sodium alginate 80 - 120", manufactured by Fujifilm Wako Pure Chemical Corporation

[0189] As is clear from Table 1 above, the slurry for a positive electrode of an electricity storage device prepared using the composition for an electricity storage device according to the present invention shown in Examples 1 to 10 was able to preferably bind active materials to each other as compared with the cases of Comparative Examples 1 to 5, and a positive electrode for an electricity storage device having good charge-discharge durability characteristics was obtained. The polymer particles (A) contained in the composition for an electricity storage device of Examples 1 to 10 shown in Table 1 above have a part of the hydroxyl groups in the repeating unit protected by a protecting group. Since the protecting group was deprotected by the hydroxide ions generated by the contact between the liquid medium (B) and the active material and the hydroxide ions in the system could be consumed, it is presumed that corrosion of the electrode surface could be suppressed. As a result, it is presumed that a low resistance could be achieved and good charge-discharge durability characteristics were exhibited.

[0190] Also, as is clear from the results in Table 2 above, in the slurry for a positive electrode of an electricity storage device prepared using the composition for an electricity storage device according to the present invention shown in Examples 11 to 21, the active materials could be more preferably bound to each other by using the polymer particles (A) in combination with a thickener rather than using the polymer particles (A) alone, and moreover, it was found that the adhesion between the active material layer and the current collector could be maintained in a better state.

[0191] Furthermore, as is clear from the results in Table 3 above, according to the slurry for a negative electrode of an electricity storage device prepared using the composition for an electricity storage device according to the present invention shown in Examples 22 to 31, good results were also shown even when a negative electrode active material was used. The polymer particles (A) contained in the composition for an electricity storage device of Examples 22 to 31 shown in Table 3 above have a part of the hydroxyl groups in the repeating unit protected by a protecting group. The protecting group was deprotected by the hydroxide ions generated by the contact between the liquid medium (B) and the active material and the hydroxide ions in the system could be consumed, hydrolysis of CMC or alginic acid used as a thickener was suppressed, and the dispersion of the active material and the filler could be made good, so it is considered that excellent adhesion strength was exhibited. Furthermore, since the coating property of the polymer particles (A) on the active material could be maintained at a high level, electrode expansion was suppressed, and as a result, it is presumed that good charge-discharge durability characteristics were exhibited.

[0192] Further, as is clear from the results in Table 4 above, in the slurry for a negative electrode of an electricity storage device prepared using the composition for an electricity storage device according to the present invention shown in Examples 32 to 38, by using the polymer particles (A) in combination with a thickener rather than using the polymer particles (A) alone, the active materials can be more suitably bound to each other, and moreover, it has been found that the adhesion between the active material layer and the current collector can be maintained in a better state.

[0193] The present invention is not limited to the above-described embodiments, and various modifications are possible. The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations having the same functions, methods, and results, or configurations having the same objectives and effects). The present invention also includes configurations in which non-essential parts of the configurations described in the above embodiments are replaced with other configurations. Furthermore, the present invention includes configurations that exhibit the same operational effects as the configurations described in the above embodiments or configurations that can achieve the same objectives. Furthermore, the present invention also includes configurations in which known techniques are added to the configurations described in the above embodiments.

Claims

1. A composition for an electric storage device, comprising polymer particles (A) and a liquid medium (B), wherein when the total of the repeating units contained in the polymer particles (A) is 100% by mass, the polymer particles (A) contain 5 to 50% by mass of a repeating unit (a1) derived from an unsaturated carboxylic acid ester having a hydroxyl group, 50 to 90% by mass of a repeating unit (a2) derived from an unsaturated carboxylic acid ester (excluding the unsaturated carboxylic acid ester having a hydroxyl group), and at least a part of the hydroxyl groups contained in the unsaturated carboxylic acid ester having a hydroxyl group is protected by a protecting group.

2. The composition for an electric storage device according to claim 1, wherein the number average particle diameter of the polymer particles (A) is 50 nm or more and 1000 nm or less.

3. The composition for an electric storage device according to claim 1 or 2, wherein the protecting group is deprotected by the action of a base.

4. The composition for an electric storage device according to any one of claims 1 to 3, wherein the protecting group is an acyl group.

5. The composition for an electric storage device according to any one of claims 1 to 4, wherein the polymer particles (A) further contain 1 to 20% by mass of a repeating unit (a3) derived from an unsaturated carboxylic acid.

6. The composition for an electric storage device according to any one of claims 1 to 5, wherein the polymer particles (A) further contain 1 to 30% by mass of a repeating unit (a4) derived from an aromatic vinyl compound.

7. The composition for an electric storage device according to any one of claims 1 to 6, wherein the surface acid amount of the polymer particles (A) is 0.05 mmol / g or more and 6 mmol / g or less.

8. The composition for an electric storage device according to any one of claims 1 to 7, wherein the swelling ratio when the polymer particles (A) are immersed in a solvent composed of propylene carbonate and diethyl carbonate at a volume fraction of 1:1 at 70°C for 24 hours is 130% by mass or more and 350% by mass or less.

9. The composition for an electric storage device according to any one of claims 1 to 8, wherein the liquid medium (B) is water.

10. A slurry for an electric storage device electrode, comprising the composition for an electric storage device according to any one of claims 1 to 9 and an active material.

11. The slurry for an electric storage device electrode according to claim 10, further comprising a thickener.

12. The slurry for a storage device electrode according to claim 10 or claim 11, containing at least one selected from the group consisting of an olivine-type lithium-containing phosphate compound, lithium cobaltate, lithium nickelate, lithium manganate, and lithium nickel cobalt manganate as the active material.

13. The slurry for a storage device electrode according to claim 10 or claim 11, containing a lithium compound and a silicon compound having oxygen as the active material.

14. A storage device electrode comprising a current collector and an active material layer formed by applying and drying the slurry for a storage device electrode according to any one of claims 10 to 13 on the surface of the current collector.

15. A storage device comprising the storage device electrode according to claim 14.

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